1. Field of the Invention
The present invention relates to an optical module which is mounted in a portable electronic appliance such as a card type digital camera or a camera-attached telephone, and is equipped with an optical element movable for focus adjustment, zooming, or the like, and a camera module using the same.
2. Description of the Related Art
Japanese Patent Publication No. 3031127 discloses a lens driving apparatus for moving a lens in an extension direction of an optical axis (hereinafter, referred to as an “optical axis direction”). As disclosed in Japanese Patent Publication No. 3031127 (Para. 0007–0009, and FIGS. 1 to 3), this lens driving apparatus includes a motor provided with a lead screw as a rotating shaft thereof, a lens holding frame slidable along a guide shaft extending in the optical axis direction, and a nut mounted to the lens holding frame such that the nut is substantially integrated with the lens holding frame. The lead screw is threadedly coupled to the lead screw, so that the lens holding frame, which holds a lens, is moved in the optical axis direction as the nut moves in the optical axis direction in accordance with rotation of the lead screw.
Also, Japanese Unexamined Patent Publication No. 2002-296480 discloses a lens driving apparatus. As disclosed in Japanese Unexamined Patent Publication No. 2002-296480 (Para. 0023–0030, and FIGS. 1 to 4), this lens driving apparatus includes a motor provided with a lead screw as a rotating shaft thereof, a nut plate threadedly coupled to the lead screw such that the nut plate is movable in the optical axis direction, and a lens holding frame in contact with the nut plate and slidable along a guide shaft extending in the optical axis direction. The lens holding frame is urged against the nut plate by elastically urging means. In accordance with rotation of the lead screw, the nut plate and the lens holding frame which holds a lens slide along the guide shaft, so that the lens is moved in the optical axis direction.
In such a case, generally, two radial bearings are arranged on the rotating shaft of the motor at positions spaced apart from each other by a certain distance, for example, upper and lower shaft end portions in the motor, respectively, so as to support the rotating shaft such that the rotating shaft does not rock.
Also, Japanese Unexamined Patent Publication No. Heisei 2-65650 discloses a structure wherein two radial bearings are arranged at upper and lower portions of a lead screw, respectively (FIG. 4 of the Publication).
In accordance with the techniques disclosed in all the above publications, a lead screw is provided, as a rotating shaft, at a driving motor, and a nut member such as a nut or a nut plate is moved in an optical axis direction in accordance with rotation of the lead screw. Meanwhile, the rotating shaft of the motor is supported by a motor frame via a pair of bearings arranged to be spaced apart from each other. By virtue of such 2-point support, the rotating shaft is maintained in a substantially uninclined state.
Accordingly, in the structure in which the nut is substantially integrated with the lens holding frame, as in Japanese Patent Publication No. 3031127, creaking or scratching may occur between the lens holding frame, which is moved via the nut in accordance with rotation of the lead screw, and the guide shaft, which guides the lens holding frame, due to a parallelism or position deviation between the lead screw and the guide shaft. In order to prevent such a phenomenon, an assembly process capable of minimizing the deviation is needed. In particular, it is necessary to mount the motor with a high accuracy. Thus, the assembly process becomes very difficult.
On the contrary, the technique of Japanese Unexamined Patent Publication No. 2002-296480 wherein the nut member (nut plate) and the lens holding frame are separated, is advantageous in that there is little influence caused by the above-mentioned deviation. In this technique, however, the nut plate must be prevented from rotating. To this end, a through hole, which is formed at the nut plate, is slidably fitted around the guide shaft. In this case, the nut plate is threadedly coupled, at one end thereof, to the lead screw, and is fitted, at the other end thereof, around the guide shaft, so that the assembly of the nut plate requires much trouble. Also, it is unsuitable to implement an automatic assembly process.
Meanwhile, since there is a gap between the fitting portion of the nut plate and the guide shaft, even though the gap is slight, the nut plate momentarily performs a slight movement as the portion of the nut plate threadedly coupled to the lead screw functions as a rotation center when the motor operates initially. In this connection, since the lens holding frame is urged against the nut plate by the elastic urging force of the elastic urging means, an increase in friction loss may occur due to the slight movement, depending on the surface accuracy of the nut plate and lens holding frame at the contact portions thereof.